Final answer:
Meselson and Stahl supported Watson and Crick's double-helix model by proving that DNA replication is semi-conservative.
Step-by-step explanation:
Meselson and Stahl supported Watson and Crick's double-helix model by proving that DNA replication is semi-conservative. In their experiment, Meselson and Stahl used density differences in nitrogen isotopes to investigate replication. Their findings showed that each newly replicated molecule of DNA consists of one 'old' strand and one 'new' strand, supporting the idea that the original information encoded in each parental strand is conserved in the daughter molecules.